In cyclic vomiting syndrome (CVS), people experience bouts or cycles of severe nausea and vomiting that last for hours or even days and alternate with longer periods of no symptoms. CVS occurs mostly in children, but the disorder can affect adults, too.

CVS has no known cause. Each episode is similar to the previous ones. The episodes tend to start at about the same time of day, last the same length of time, and present the same symptoms at the same level of intensity. Although CVS can begin at any age in children and adults, it usually starts between the ages of 3 and 7. In adults, episodes tend to occur less often than they do in children, but they last longer. Furthermore, the events or situations that trigger episodes in adults cannot always be pinpointed as easily as they can in children.

Episodes can be so severe that a person may have to stay in bed for days, unable to go to school or work. No one knows for sure how many people have CVS, but medical researchers believe that more people may have the disorder than is commonly thought (as many as 1 in 50 children in one study). Because other more common diseases and disorders also cause cycles of vomiting, many people with CVS are initially misdiagnosed until the other disorders can be ruled out. What is known is that CVS can be disruptive and frightening not just to people who have it, but to the entire family as well.